When fixing a board in position within the casing of a personal computer or the like, it is necessary for the board to be spaced apart from the inner side surface of the casing by a predetermined dimension in order to prevent confinement of heat, a shock from the outside, etc. Thus, as shown in FIG. 2, a spacer nut 12 formed in a substantially cylindrical configuration is forced into an inner side surface 11 of a casing 10 and fixed in position so as to be erect, and a screw passing hole portion 14 previously provided in a board 13 and the spacer nut 12 are matched with each other; then, the board 13 is placed on the spacer nut 12, and the board 13 and the spacer nut 12 are fixed to each other by a screw 15, whereby the board 13 and the inner side surface 11 of the casing 10 are spaced apart from each other by a dimension corresponding to the height of the spacer nut 12.
As shown in FIG. 3, generally speaking, the spacer nut 12 includes a shaft portion 16 of a substantially cylindrical overall configuration, and a flange portion 17 arranged at a proximal end portion of the shaft portion 16, with a gear-like serration portion 18 being formed in the outer periphery of the flange portion 17.
Further, a circumferentially extending groove portion 19 is formed in the outer periphery of the proximal end portion of the shaft portion 16, and a thread groove 22 that can be threadedly engaged with the screw 15 (not shown in FIG. 3) is formed in an inner peripheral surface portion 21. Due to the provision of the serration portion 18 and the groove portion 19, the material of the casing 10 enters trough portions 20 of the serration portion 18 and the groove 19 as shown in FIG. 2 when the spacer nut 12 is forced into the casing 10, thereby enabling the spacer nut 12 to be firmly fixed to the casing 10.
The spacer nut of the above configuration has been generally produced by using an NC lathe by the following procedures:
(1) A serration portion is formed by knurling in the entire area of the outer peripheral surface portion of a cylindrical bar material formed in a diameter somewhat larger than that of the spacer nut to be produced.
(2) The bar material is cut in a predetermined length dimension as appropriate according to the kind of spacer nut to be produced.
(3) After the cutting, the material is rotated circumferentially around the axis of the cylinder, and the portion of the serration portion other than that constituting the flange portion is cut off to form the shaft portion, and, at the same time, the groove portion is formed by cutting at the proximal end portion of the shaft portion.
Since the above cutting operations are performed by using an NC lathe, it is possible to secure a high machining precision.
However, an NC lathe is generally rather expensive, and has a problem in that it involves a very large introduction cost when it is newly introduced as equipment.
Further, since the material is a cylindrical bar material, it cannot be formed into a roll shape as in the case of a metal plate material. Thus, due to restrictions in terms of handling, there is used a material previously cut in a length dimension of approximately 1 to 2 meters.
Thus, in the machining operation, it is necessary to newly replenish a bar material as appropriate, resulting in a rather poor production efficiency; further, since it is necessary to previously machine the material into a cylindrical shape, the material supply cost involved is rather high.
Despite the above-mentioned problems, there has been proposed until now no effective manufacturing method to take the place of the manufacturing method using an NC lathe.